(A) Field of the Invention
The present invention relates to a structure for composite materials of a positive temperature coefficient thermistor and a method of making the same, and in particular, to a conductive polymeric composite material having carbon black utilized to a structure for composite materials of a positive temperature coefficient thermistor and a method of making the same.
(B) Description of Related Art
Thermistor devices are already widely used in many fields, such as temperature detection, security control, temperature compensation, and so on. In the past, a thermistor device has mainly utilized ceramic material. However ceramic material needs to be manufactured at high temperatures, in most cases, more than 900xc2x0 C. Thus the energy consumption is enormous, and the process is very complicated. Later on, a thermistor device utilizing a polymeric substrate is developed. As the manufacturing temperature of a thermistor device employing a polymeric substrate can be lower than 300xc2x0 C., its manufacturing and molding are easier, the energy consumption is less, the process is easier, and the production cost is lower. Thus its application gets more and more popular as time goes on.
The conductive crystallized polymeric composite material filled with carbon black is under a low resistance status at a room temperature due to its characteristics of the positive temperature coefficient thermistor. When the current flowing though the conductive crystallized polymeric composite material filled with carbon black is too large, and the temperature of the conductive crystallized polymeric composite material filled with carbon black reaches the melting point of polyethylene, volumes of resin in the conductive crystallized polymeric composite material filled with carbon black expand to an extent that makes the conductive stuffing materials in the conductive crystallized polymeric composite material filled with carbon black break down from a continuous status to a discontinuous status. Thus the resistance of the conductive crystallized polymeric composite material filled with carbon black will rise rapidly, and plaques made of conductive crystallized polymeric composite material filled with carbon black will break the current accordingly. So plaques made of conductive crystallized polymeric composite material filled with carbon black can be applied to the multi-layer circuit laminated structure for designing an over-current protection device and a temperature switch device.
However, the interfacial joint strength of the plaques made of the metal foil and conductive crystallized polymeric composite material filled with carbon black is not good enough after the thermal laminating process. Besides, the joint of conductive crystallized polymeric composite material filled with carbon black and metal foil is formed by use of the heating resin, which inside the conductive crystallized polymeric composite material filled with carbon black, flows. Thus, the metal electrodes surface of metal laminated material as well as vacancy among the conductive carbon particles of conductive polymeric composite material are filled with carbon black. However, the carbon black cannot fully contact with the metal electrodes of the metal laminated plaque, and thus the interfacial resistance between metal laminated plaque and the conductive crystallized polymeric composite material plaque filled with carbon black rises. Moreover, when a laminated structure of the multi-layer circuit is used to fabricate an over-current protection device or a temperature switch device, it has to face various kinds of regular or irregular temperature variation. This leads to problems of joints between the electrodes of the metal laminated plaque and the conductive crystallized polymeric composite material plaque filled with carbon black.
To solve the problems of joint strength and interfacial resistance, U.S. Pat. Nos. 4,689,475 and 4,800,253 utilize electroplating for forming a rough surface with metal nodular protrusions on the surface of metal foil to increase the joint strength of the metal electrodes and the conductive crystallized polymeric composite material plaque filled with the carbon black.
However, the techniques disclosed by theses patents use the carbon black to be directly wedged to metal nodular protrusions, and the geometric shapes of the carbon black and of metal nodular protrusions are different, so the contact density is not very well. Meanwhile, mobility of resin on the surface of carbon black is not good between carbon black and metal, the resin can just be adhered to the surface of the metal and thus, increase the interfacial resistance and effect its function.
Furthermore, a known fabrication method of a thermistor is to make the conductive crystallized polymeric composite material filled with carbon black adhere to a foil, such as a copper foil or nickel foil. The method is subjected to the foil material to proceed with a continuous electroplating process for a whole roll of foil, so that the fabrication method is limited.
An object of the present invention is to provide a structure for composite materials of a positive temperature coefficient thermistor device and a method of making the same for forming a fine joint between metal electrodes and the polymeric composite material plaque having carbon black.
Another object of the present invention is to provide a structure for composite materials of a positive temperature coefficient thermistor device and a method of making the same for lowering down the interfacial resistance between metal electrodes and the polymeric composite material plaque having the carbon black.
Yet another object of the present invention is to provide a structure for composite materials of a positive temperature coefficient thermistor device and a method of making the same, which can fit into the well-developed printed circuit board process and utilize the plaque fabrication method. Thus the process can be simpler.
To achieve the objects described above and other effects, the present invention provides a structure for composite materials of a positive temperature coefficient thermistor device and a method of making the same. The method comprises the step of providing a metal laminated material with metal layers on its top and bottom surfaces and an insulating layer as its middle layer, and a conducting through hole between the top metal layer and the bottom metal layer is provided for conducting. Then the carbon black is electroplated onto the surface of the top metal layer. Because of the electroplated carbon black, a continuous porous structure is formed. Moreover, a conductive crystallized polymeric composite material filled with the carbon black is hot laminated with the surface of the top metal layer having the continuous porous structure to form a structure for composite materials of a positive temperature coefficient thermistor device.
Because of the composite electroplating, the surface of porous structure of the top metal layer contains the carbon black already. When a hot laminating process is performed, the carbon black of the porous structure of the top metal layer can be tightly integrated with the conductive polymeric composite material having the carbon black to form a fine joint.
Moreover, because the tight integration of the carbon black of the porous structure of the top metal layer with the conductive polymeric composite material, the interfacial resistance between the metal electrodes and the conductive polymeric composite material is effectively lowered down.
Furthermore, because existing printed circuit boards can be used as the metal laminated material of the present invention, the well-developed printed circuit board process can be used directly in the process of the thermistor device. Manufacturing the thermistor device by means of the plaque fabrication method of the printed circuit board process is simpler than the presently used continuous electroplating process for the whole roll of soft foil, and the process can be greatly simplified accordingly.
The present invention also provides a composite material laminated structure. The composite material laminated structure comprises a first metal layer; an insulating layer disposed on the first metal layer; and a second metal layer which is further disposed on the insulating layer. In the structure, one side of the second metal layer is a porous structure having a secondary aggregate of carbon black; wherein a conducting through hole is disposed between the second metal layer and the first metal layer through the insulating layer, the conducting through hole is used for electrical conduction between the first metal layer and the second metal layer. Moreover, a conductive crystallized polymeric composite material layer filled with carbon black is disposed on the second metal layer having a porous structure.
The present invention further provides a method for manufacturing a composite material laminated structure having a metal layer, the method first provides a metal laminated material having an insulating layer disposed at its bottom, and then electroplating a carbon black onto a surface of a metal layer of the metal laminated material by a composite electroplating process to form a continuous porous structure on the surface of the metal layer. After the continuous porous structure is formed, thermal-laminating a conductive crystallized polymeric composite material filled with carbon black with the surface of the metal layer having the continuous porous structure, thus a composite material laminated structure having a metal layer is formed.
Still another model provided by the present invention is a structure for composite materials of positive temperature coefficient thermistor device, the structure comprises an insulating layer; a first metal layer disposed on the insulating layer; a first composite material layer further disposed on the first metal layer, and a second composite material layer. The first composite material layer is taken as a metal basis having a secondary aggregate of carbon black which has a metal on its surface. A second composite material layer is disposed on the first composite material layer, the second composite material layer being comprised of the conductive crystallized polymeric composite material layer filled with carbon black.
In addition to the structure described above, the structure of the model further comprises a second metal layer disposed below the insulating layer. The materials of the metal layer, the insulating layer, and the second metal layer are all two-sided foil substrate, and a conducting through hole is disposed between the metal layer and the second metal layer as the electrical conduction between the metal layer and the second metal layer.